1. Field of the Invention
The present invention relates to a backlighting system for a LCD type display. More specifically, the present invention relates to a backlighting system which monitors the brightness of the backlight illumination and which gradually increases the power supplied to the backlight in order to compensate for the degradation of the light source lamp with the passing of time.
2. Description of the Related Art
Display technology is rapidly changing with the advent of better and brighter liquid crystal displays (LCDs). As is known, cathode ray tubes (CRTs) are being rapidly replaced by LCDs due to the size and power advantages that are possible with such arrangements.
A few short years ago, the brightness of LCDs was 2.5 times less than that possible with CRTs. However, advances in backlighting technology have enabled the development of LCD displays that now exhibit brightness that rivals that possible with CRTs. These advances have involved the use of brightness enhancing films which focus the viewable light being emitted from the screen, color polarizers which maximize the usable light coming from the backlight, and more efficient light guides.
However, one undesirable tendency in this quest for brighter displays, is to either drive the light sources at their fill rated power, or even to overdrive the same from the outset. This of course, increases the brightness that is produced, but markedly speeds up the rate of degradation of the light sources and drastically reduces the life of the lamp or lamps being used.
Accordingly, one advantage that CRT-type displays have over LCDs is that the CRT type display exhibits more consistent display brightness over its lifetime. More specifically, a CRT will decrease in brightness about 10% 15% during its lifetime due to factors relating to the electronic gun filament, phosphor degradation and the driving electronics. Depending on the type of CRT, one or all of these factors may be responsible for the reduction in brightness with the passing of time. An LCD, on the other hand, will decrease in brightness by about 50%. This reduction is, however, is directly related to the degradation of the backlighting system associated with the liquid crystal structures which actually produce the image(s).
In most instances, the backlighting for LCD type displays is provided by one or more cold cathode fluorescent lamps (CCFLs), a power inverter and a light guide. The CCFL is the only component that degrades significantly with the passing of time. Accordingly, as the user must manually adjust the level of brightness to that which is preferred, it quickly becomes apparent to the user that the rate of reduction in the brightness in LCD type displays is more pronounced than with those which are based on CRT.
Additionally, the change in brightness in a LCD equipped display, which follows a service wherein the light source(s) is replaced, tends to be much more apparent to the user than in the case wherein a new CRT is installed.
Hence, in order to make LCD displays acceptable alternatives to CRTs, it is necessary to reduce the degree by which the brightness of LCDs are perceived to vary and reduce the passing of time.